A new, small study of 25 women suggests that being mildly dehydrated can take a toll on women's mood and cognitive function. In the study, published in the latest issue of The Journal of Nutrition, researchers found that dehydration was a prime factor in causing headaches, loss of focus, fatigue, and low mood while both exercising and resting.

US magazine TIME reported last week that the women in the study experienced the bad effects from only mild dehydration about one percent lower than optimal hydration levels.

The Huffington Post also cites a 2009 study conducted by Tufts University researchers in the US that found "that dehydration leads to fatigue, confusion, and a negative mood among young female athletes."

TIME reports that while men weren't included in the research, the results likely apply to them as well.

To stay hydrated, opt for plain water or other non-alcoholic and caffeine-free drinks. While exactly how much water you need to drink daily varies and isn't well defined (some experts say eight glasses a day is too much), one good measure is to check the color of your urine "if it's darker rather than nearly clear, you need more water," writes Time.